Fossil and Relative and Absolute Dating Quiz 10 Minutes

Transcription

1 Fossils and Geologic Dating - Advanced Components and Agenda Fossil Notes- Pages 2 Watch the video and take notes. Do all organisms create fossils?- Pages 3-4 Obtain supplies from your teacher and find a partner. Follow the directions and answer the questions. Watch Fossil Video Watch the video on my website and give a three sentence summary on the back of this packet. Relative Dating Practice- Page 5-7 Sedimentary Rock Layers- Page 8 Obtain strips of paper from your teacher. Sedimentary Rock Worksheet Page 9 Complete the worksheet. Relative vs Absolute Time- Pages Complete the worksheet. Radioactive Half-life Activity- Pages Complete the radioactive half-life activity with a partner. Give your data to your teacher. Fossil Station Activity- Pages Walk around the room and answer the questions associated with each station. Fossil and Relative and Absolute Dating Quiz 10 Minutes o o o Ask any questions you might have and study your notes page Take the Types of Resources Quiz TOMORROW You cannot take the quiz the same day you finish the activity. STUDY!!! Give your Science teacher your score and percent 70% or Above (Pick one of the following) 69% or Under Continue working on the packet STUDY!!! Retake the quiz TOMORROW NAME: PERIOD: 1

2 Fossil Notes What is a fossil? Remains of once living animals or plant that represents of organisms living today Does every organism turn into a fossil? No - Normally they rot or get eaten They need perfect conditions Buried quickly / How are fossils formed? 1. Animal dies and is buried by sediment 2. Extreme pressure turns sediment into sedimentary rock 3. Skeleton dissolves and leaves a hole/mold Dissolved by ground water 4. Minerals crystallize in hole and a is formed Mineral rich water enters mold and leaves minerals 5. Millions of years later, the fossil is exposed on the Earths surface Earthquakes, building, construction, digging / drilling What do fossils tell us? Which organisms were alive in the past The diversity of the types of organisms that were present at any given time. Which organisms became extinct when (and why), How organisms have evolved over time. To see how organisms are related To see how (individual vs group) and where organisms used to live. To have a better understanding of the world around us How do we get information about fossils? Type of Fossil fossils Tell us what the animal / plant looks like Ex: Petrified wood, frozen mammoths, amber fossils Tell us what the animal did Ex. Footprints, trackways, Coprolites (poo) Age of Fossil RELATIVE DATING Approximate time scale Uses rock layers Used when fossils / rock layers in layers too old for absolute _ Information provided o Approximately when animals lived o Which animals lived in the same time periods o What natural disasters happened (earthquakes, volcanoes, droughts) and when they occurred o Think: Grand Canyon! ABSOLUTE DATING Specific time scale Uses radioactive accurate Information Provided o Specific age of the fossil o Can only be used up to 70,000 years (depending on the element used) How it Works: o Certain naturally occurring elements are radioactive and they break down at predictable rates o Scientists use these rates to measure the half-life of elements Half life = Time it takes for half the radioactive element to break down o Scientists compare the amount of an element to the initial amount and the half-life to determine age If each half-life is 5,730 years old and the sample is 2 half lives then it is 11,460 years old (2 X 5,730 = 11,460) 2

3 Do All Organisms Become Fossils? Background: Fossils are made when a living thing dies and is buried by mud, silt, volcanic ash, or sand. Fossils could also be frozen in ice, mummified in hot or cold deserts, or preserved in tar. Usually, all of a living thing's soft parts decay, leaving only the hard parts to be buried, except when a living thing is frozen or mummified. The mud, silt, and sand are called sediments. The sediments have water with minerals in it. The minerals in the water soak into the hard parts, changing them into a rock like material and preserving the hard parts as fossils. Living things which die in or near oceans, lakes, or rivers have a better chance of fossilization than those which die on dry land, because they will be quickly buried. Over thousands and millions of years the sediments form heavy layers which slowly turn into sedimentary rock. Materials: - 3 Sugar cubes - 2 pieces of clay - 1 beaker - Spoon Procedure: 1. Make sure you have each of the materials listed above. 2. Sugar Cube 1 o Take the larger piece of clay and wrap it tightly around the sugar cube so the entire cube is covered 3. Sugar Cube 2 o Take the smaller piece of clay and wrap it around the sugar cube so only HALF the sugar cube is covered 4. Sugar Cube 3 o Leave the third sugar cube alone. 5. Fill the beaker ¾ full of water 6. Place all 3 sugar cubes into the beaker of water 7. Stir the cubes in water until the uncovered sugar cube (#3) is dissolved. 8. Remove the other cubes from the water and examine the remains. 9. Observe what happens and answer the questions below. Analysis Questions: 1. What happened with sugar cube 1? Describe the sugar cube and the clay. 2. What happened with sugar cube 2? Describe the sugar cube and the clay. 3

4 3. What happened with sugar cube 3? 4. Explain when the clay worked to preserve the sugar cube. Why did this happen? 5. Explain when the clay didn t work to preserve the sugar cube. Why did this happen? 6. Explain how this activity is similar to the way fossils are formed. 7. What needs to occur to an organism in order for it to become a fossil? 8. List the ways an organism can be preserved in nature. What in nature could replace the clay? 9. What do you think the stirring could have represented? 10. In addition to what you answered for #10, what could happen to prevent an organism from becoming a fossil? 4

5 Relative Dating practice Purpose: In this activity you will learn to determine the sequence of geologic events from cross sections of strata (rocks) in a given area. Background: Before absolute dating of rocks was developed in the 20th century, geologists had to rely on relative age dating, which places geologic events in their order of occurrence. The method begins with the careful drawing and description of strata (the geologic cross section or profile). Relative age dating assumes that the lower layers in any particular cross section are older than the upper layers in that cross section ( the law of superposition ) and that an object cannot be older than the materials of which it is composed. How? In this process, you will study the rocks and events in a geologic cross section and put them in the correct order from oldest to youngest. In order to do your best on this activity, you must understand a few of the basic principles that are applicable to relative age relationships between rocks: (you do not need to know these terms but they can help you determine the correct order of the layers) Principle of superposition: in a sequence of undeformed sedimentary rocks, the oldest beds are on the bottom and the youngest are on the top. Principle of original horizontality: sedimentary layers are horizontal, or nearly so, when originally deposited. Strata that are not horizontal have been deformed by movements of the Earth s crust. Principle of faunal succession: groups of fossil plants and animals occur in the geologic record in a definite and determinable order. A period of geologic time can be recognized by its respective fossils. Principle of crosscutting relations: geologic features, such as faults, and igneous intrusions are younger than the rocks they cut. Principle of inclusion: a rock body that contains inclusions of preexisting rocks is younger that the rocks from which the inclusions came from. The easiest way to do relative age dating is to work from oldest to youngest. Try to find the oldest rock (usually located near the bottom) in the diagram below and work your way up. Directions: For each of the following cross sections, determine the relative age sequence of the rocks. Place the answers in the spaces on the right. Remember, always start by looking for the oldest rock first and working your way from oldest to youngest. Don t forget to consider all intrusions and faults! The diagrams go from simplest to hardest to let you progressively improve your skills. 5

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7 Youngest Oldest Youngest Oldest CHALLENGE: (not for grade) Youngest Oldest 7

8 Sedimentary Rock Layers Over millions of years, sediments such as sand and silt were laid down and compressed to form sedimentary rock layers. They preserve a record of ancient landscapes, climates, and organisms. Scientists often determine the correct sequence of sedimentary rock layers using the fossils found within them. They compare the fossils to figure out if two layers are from the same geologic time period, or if one layer is older than the other. Procedure: 1. Cut out the five strips and place them in order a. Order i. Youngest at the top ii. Oldest at the bottom b. Hint: i. Organisms do not disappear for a layer and then reappear 2. Glue the strips in order below Analysis Questions: 1. Which organisms survived the entire time? 2. Which organisms became extinct? 3. Could Tarbosaurus have hunted Seismosaurus? Why or why not? 8

9 Sedimentary Rock Worksheet Sedimentary rocks are particularly important in the understanding of the Earth s history. These rocks are formed at the Earth s surface as layers of sediment (small particles broken down from other rocks) build up, and pressure compresses them into rock. Each layer of rock records the nature of the environment at the time that it was laid down. The layers are the characteristic feature of sedimentary rocks, the oldest ones being located at the bottom of the sequence as they were deposited first. Fossils are probably the most important inclusions found in sedimentary rocks. Knowing something about these prehistoric life-forms and the rock they are found in can help us to recreate environments and ecosystems from the past. Use the pictures on the right to answer the following questions. 1. Which shell is the oldest? 2. There are no shells in Layer 3, why might this be? 3. No dinosaur bone is found below Layer 2, this might mean: 4. If you also found a softdrink can in Layer 3, what could you say about Layers 3, 4, & 5? 5. Are there likely to be dinosaur bones in any of these layers? Explain. Sometimes rocks are reshaped as a result of movement. This can be seen when rock layers are not simple straight layers or no longer match up. Faulting occurs when the rock layers move along a weak point or fault line. Fossils are sometimes used to match layers that are no longer contiguous. Some folded or faulted formations may then be eroded to a flat surface before more layers of sediment are deposited on the surface. This is called an unconformity 6. In diagram I, which layer is the same as Layer A? 7. In diagram II, which layers do you think were laid down in the Ocean? Which were deposited on or near land? 8. What can you say about the top layer in diagram I? 9

10 Relative vs. Absolute Time Background: By knowing the age of the rock that a fossil is found in, geologists can usually tell the age of the fossil. Sometimes they cannot give it an exact date, but they know that it is older or younger than another fossil. Dating a fossil by saying it is older or younger than another fossil is called relative dating. If the geologists know the exact age of a fossil, they usually express its age in millions of years ago (mya) that it was formed. Scientists use radioactive half-life data to determine a fossils age. Dating a fossil by assigning it a specific age is called absolute dating. Procedure: 1. Make a relative time scale out of 7-8 events that have occurred in your life. a. Ex. Include important events such as your birth, something you did today, starting kindergarten, and losing your first tooth. b. REMEMBER: These events only show chronological order, NOT exact dates 2. Using your relative scale, make an absolute time scale by adding dates 3. Answer the analysis questions below Example: Example Time Scale Relative Time Scale Absolute Time Scale I was born. I was born. August 21, 1985 I took my first steps. I took my first steps July 15, 1986 My little sister was born My little sister was born May 30, 1988 First high school RBI First high school RBI March 21, 2001 Graduated high school Graduated high school May 28, 2004 Graduated college Graduated college May 31, 2008 Got my first job Got my first job August 26, 2009 Today Today November 30,

11 My Time Scale: Example Time Scale Relative Time Scale I was born. I was born. Absolute Time Scale Today Today Analysis Questions: 1. Describe how we determine relative time. 2. Describe how we determine absolute time. 3. Why are both relative time and absolute time to reconstruct past timescales? 11

12 Radioactive Half-Life Background: One characteristic of radioactive material is that radioactive isotopes spontaneously give off particles. This process, called radioactive decay, changes the nucleus of the material. The length of time it takes for half of a sample of radioactive material to decay is called the half-life. Each radioactive isotope has a characteristic halflife, ranging from less than a second to millions of years. Carbon-14 is a special unstable element used in the absolute dating of material that was once alive, such as fossil bones. Every 5,730 years, half of the carbon-14 in a fossil specimen decays or breaks down into a more stable element. In this activity, you will use pennies that can land heads up (nuclei that have undergone radioactive decay) or tails up (nuclei that haven t yet decayed) as a simplified model of half-life. Procedure: 1. Trail 1 a. Count to make sure you have 100 pennies b. Shake the pennies up in the cup and roll them into the box lid c. Count how many pennies are heads up and record the data below d. Remove all of the pennies that are heads up. e. Repeat steps 2-4 five more times 2. Trail 2 and 3 a. Repeat each of the steps above 3. Average your data from the three trials 4. Subtract your average from 100 to get the average removed 5. Type your averages in the class excel document 6. Graph the CLASS DATA below 7. Answer the analysis questions Data: Round Trail 1 INDIVIUDAL DATA Trail 2 Trial 3 Average Pennies Remaining Average Pennies Removed Round 0 0 CLASS DATA Class Average Pennies Remaining Class Average Pennies Removed

13 Analysis Questions: 1. What did the pennies represent? 2. What did each trial represent? 3. What pattern do you notice? 4. How does your data compare to the class data? 5. Compare your graph with the Half-life of Carbon-14 graph on the right. What similarities do you see? 6. Why is radioactive decay helpful for determining the age of fossils? 7. If a sample of pennies contained 75 heads and 25 tails, how many half-lives would have passed since the sample formed. Explain your answer. 8. If each half-life was 2000, years how many years old would the above sample be? 13

14 Fossil Station Activity Station 1 1. Why do you think we cannot actually replicate this procedure in real life? Station What are 2 things fossils tell us? 3. Which is better for creating a fossil: remains that are buried quickly or slowly? 4. Why? 5. How do decomposers stop a fossil from being created? 6. Do organisms have to be buried to become a fossil? Explain. 7. Why do you think we do not find fossils for things like worms? 8. How do fossils get destroyed? Station 3 9. Compare and contrast fossil A and B (use appearance and fossil type) 10. Identify each fossil type at your station Fossil A: Fossil B: Fossil C: Station Compare and contrast fossil A and B (use appearance and fossil type) 14

15 12. Identify each fossil type at your station Fossil A: Fossil B: Station Do you think it is beneficial for scientists to continue their research on the fossil record? 14. Why? Station Diagram 1: Identify the layers from OLDEST to YOUNGEST 16. Diagram 2: Identify the layers from OLDEST to YOUNGEST Station Complete the following chart Grams of C-14 Amount of time that has passed (years) Number of half lives Station How might studying fossils help us in uncovering changes that have occurred in the world around us and to particular animals? (TURN OVER FOR ANOTHER STATION) 15

16 Station The following fossil was located 200 miles above sea level on a mountain. Compare its original environment to its current one and explain how it got here. a. Original environment: b. Current environment: c. How did it get here? Station 11 In an article summary published in Science Daily, some paleontologists believe that species becoming extinct today may not be known to future generations. The reason for this is that they will vanish from the fossil record. Animals that will be impacted the most are small animals and birds. 20. Why do you think these species would not be present in the fossil record in the future? Give at least 2 reasons. 21. Do you think that there were plants and animals in the past that we will never know existed? Why or why not? Discuss your answer with another student and present your answer to your teacher. 16